The present invention relates generally to agricultural harvesters and, more specifically, to a height control for harvester row units.
Harvesters such as cotton pickers include row units supported for vertical movement by lift arms controlled by hydraulic lift cylinders. Extension and retraction of the lift cylinders is controlled by spool valves connected to height sensing skids on the row units, such as shown in commonly assigned U.S. Pat. No. 5,519,988. Electrohydraulic valves provide an on/off function for oil flow to and from the cylinders. During field operations with the electrohydraulic valves in the on position, the skids mechanically move the spools to extend the cylinders when any unit is too low and retract the cylinders when all the units are too far above the surface of the field.
Present systems of the type shown in the aforementioned patent have complex hydraulic plumbing which is difficult and time-consuming to connect and maintain. In addition, adjustments of the operating height to provide efficient picking and prevent grounding are relatively difficult. System sensitivity and response time are not easily changed since linkage and internal hydraulic revisions are required. Maintaining good reliability and stability with the complex plumbing systems and mechanical linkages has been a continuing problem.
It is therefore an object of the present invention to provide an improved height control system for a harvester row unit. It is a further object to provide such a unit which overcomes most or all of the aforementioned problems.
It is a further object to provide such an improved harvester row unit height control system with simplified and more reliable hydraulic plumbing compared to at least most available systems.
It is another object to provide such a harvester height control system which is less expensive and more reliable than most systems. It is still another object to provide such a system which has improved sensitivity and adjustability.
It is yet another object of the invention to provide a row unit height control system for a cotton harvester having improved reliability, sensitivity and adjustability. It is a further object to provide such a system which is less complex and costly than many previously available cotton harvester height control systems.
The improved hydraulic lift and height control system for a harvester includes electrohydraulic proportional valves to eliminate linkage-actuated valves. A single set of proportional valves connected to height control cylinders and to a controller provides manual or automatic harvester row unit height control. The controller receives inputs from a manual raise/lower switch, a rate response potentiometer, and height control potentiometers in the cab. Signals are also received from row unit height sensing transducers, a tachometer and shaft monitor. The operator actuates the raise/lower switch, which is conveniently located on the hydro control handle, to control extension and retraction of cylinders for movement of the row units between a raised transport position and a lowered field operating position. In the lowered position, the controller compares the signals from the height sensing transducers with the signals from the height control potentiometers and sends an electrical control signal to the proportional valves to maintain the row units at the height selected by the operator. The magnitude of the control signal and thus the rate of correction of height are determined by the rate response potentiometer and the amount of variation between the actual and desired row unit height. The controller prevents automatic operation if the relay to engage the row units is not turned on, and lowering of the row units is inhibited if the tachometer signal indicates the engine is not running.
The hydraulic control circuit includes a first proportional valve connected between a source of hydraulic fluid under pressure and the base end of a single acting cylinder to control cylinder extension for raising a set of row units, and a second proportional valve connected between the base end of the cylinder and a return to sump line to control cylinder retraction for lowering the set of row units. A low leakage, electrically controlled on-off valve is connected in series with a second proportional valve and has a normally closed position to prevent unwanted row unit lowering. The controller is connected to the on-off valve and provides a signal for turning the valve on for normal harvester operation.
These and other objects, features and advantages of the present invention will become apparent to one skilled in the art upon reading the following detailed description in view of the drawings.